U.S. patent application number 16/610966 was filed with the patent office on 2020-04-02 for soldering device and a method for producing a solder connection of components using adhesive material for temporary connection o.
This patent application is currently assigned to PINK GmbH Thermosysteme. The applicant listed for this patent is PINK GmbH Thermosysteme. Invention is credited to Aaron Hutzler, Christoph Oetzel.
Application Number | 20200101549 16/610966 |
Document ID | / |
Family ID | 62116885 |
Filed Date | 2020-04-02 |
United States Patent
Application |
20200101549 |
Kind Code |
A1 |
Hutzler; Aaron ; et
al. |
April 2, 2020 |
SOLDERING DEVICE AND A METHOD FOR PRODUCING A SOLDER CONNECTION OF
COMPONENTS USING ADHESIVE MATERIAL FOR TEMPORARY CONNECTION OF THE
COMPONENTS
Abstract
The invention relates to a method for producing a solder
connection between a plurality of components (12A, 12B) in a
process chamber (74) sealed off from its surroundings by heating
and melting solder material (16) which is arranged between the
components (12A, 12B) to be connected. It is proposed that the
components (12A, 12B) to be connected are provisionally connected
with a bonding material (18) to form a solder group (10) in which
the components (12A, 12B) are fixed relative to one another in a
joining position.
Inventors: |
Hutzler; Aaron; (Nurnberg,
DE) ; Oetzel; Christoph; (Wertheim, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PINK GmbH Thermosysteme |
Wertheim |
|
DE |
|
|
Assignee: |
PINK GmbH Thermosysteme
Wertheim
DE
|
Family ID: |
62116885 |
Appl. No.: |
16/610966 |
Filed: |
May 7, 2018 |
PCT Filed: |
May 7, 2018 |
PCT NO: |
PCT/EP2018/061727 |
371 Date: |
November 5, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 2224/17181
20130101; H01L 2224/75301 20130101; B23K 3/087 20130101; H01L
2224/16145 20130101; H01L 2224/81801 20130101; H01L 2224/83911
20130101; H05K 3/305 20130101; H01L 2224/9211 20130101; H01L
2224/83203 20130101; B23K 1/20 20130101; H01L 24/17 20130101; H01L
24/32 20130101; H01L 2224/33181 20130101; H01L 2225/06513 20130101;
H01L 2224/81911 20130101; H01L 2224/75252 20130101; H01L 2224/32145
20130101; B23K 1/206 20130101; H01L 24/81 20130101; H01L 2224/81203
20130101; B23K 1/0016 20130101; B23K 2101/42 20180801; H01L 24/92
20130101; H01L 2224/7501 20130101; H01L 24/16 20130101; H01L
2224/73253 20130101; H01L 2224/83801 20130101; H01L 2224/73204
20130101; H05K 3/3494 20130101; H05K 2203/0278 20130101; B23K
37/0443 20130101; H01L 24/33 20130101; H01L 24/83 20130101; H01L
25/50 20130101; H01L 24/75 20130101; H01L 25/0657 20130101; H01L
24/73 20130101; H01L 2224/73204 20130101; H01L 2224/16145 20130101;
H01L 2224/32145 20130101; H01L 2924/00 20130101 |
International
Class: |
B23K 3/08 20060101
B23K003/08; B23K 1/00 20060101 B23K001/00; B23K 1/20 20060101
B23K001/20; H01L 23/00 20060101 H01L023/00; H01L 25/00 20060101
H01L025/00; H01L 25/065 20060101 H01L025/065 |
Foreign Application Data
Date |
Code |
Application Number |
May 5, 2017 |
DE |
10 2017 109 747.3 |
Aug 28, 2017 |
DE |
20 2017 105 174.9 |
Claims
1.-18. (canceled)
19. A method for producing a solder connection between a plurality
of components in a sealed process chamber, the method comprising:
heating a solder group to an intermediate temperature, the solder
group comprising solder material between the plurality of
components and a bonding material, wherein the intermediate
temperature is lower than a melting temperature of the solder
material at atmospheric pressure; reducing a pressure in the
process chamber above an evaporation pressure of the bonding
material at the intermediate temperature; introducing a cleaning
agent into the process chamber to clean the solder group, the
cleaning agent comprising methanoic acid, hydrogen, or a plasma;
reducing the pressure in the process chamber below the evaporation
pressure of the bonding material at the intermediate temperature
such that the bonding material evaporates.
20. The method of claim 19, wherein the bonding material is
selected such that the bonding evaporates during production of a
solder connection.
21. The method of claim 20, wherein, when the evaporation pressure
is lower than the atmospheric pressure, an evaporation temperature
of the bonding material is lower than the melting temperature of
the solder material.
22. The method of claim 19, further comprising maintaining the
intermediate temperature while reducing the pressure in the process
chamber below the evaporation pressure of the bonding material at a
predetermined temperature value or within a predetermined
temperature range at least until evaporation of the bonding
material is complete.
23. The method of claim 19, wherein the bonding material is
arranged in a region comprising one or more of an edge, a corner,
and a center of the plurality of components or the solder
material.
24. The method of claim 19, wherein the solder material melts after
the bonding material evaporates.
25. The method of claim 19, wherein the bonding material is liquid
or pasty and comprises a terpene alcohol.
26. The method of claim 25, wherein the terpene alcohol is
isobornyl cyclohexanol.
27. A process chamber for producing a solder connection between a
plurality of components using a solder group comprising a solder
material, the process chamber comprising: a soldering apparatus
comprising: a base plate, a pressure plate, and a stop apparatus,
wherein: the base plate and the pressure plate are adjustable
relative to one another with regards to spacing between the base
plate and the pressure plate for exerting a pressure force on the
solder group received between the base plate and the pressure
plate, and the stop apparatus limits a spacing between the base
plate and the pressure plate to a minimum spacing such that, once
the solder material in the solder group has melted, the solder
group has a predetermined thickness.
28. The process chamber of claim 27, wherein the stop apparatus is
arranged on the base plate or the pressure plate.
29. The process chamber of claim 27, wherein the stop apparatus is
adjustable such that the minimum spacing can be set.
30. The process chamber of claim 27, wherein the stop apparatus
comprises a plurality of length-adjustable stop elements.
31. The process chamber of claim 30, wherein each of the plurality
of length-adjustable stop elements comprises an adjusting device
that interacts with a complementary adjusting device provided on
the base plate or the pressure plate.
32. The process chamber of claim 30, wherein the plurality of
length-adjustable stop elements are arranged such that, upon
reaching the minimum spacing, the plurality of length-adjustable
stop elements bear a respective free end against a component of the
solder group, against a base frame carrying one of the components,
or against the base plate.
33. The process chamber of claim 27, wherein at least one of the
base plate and the pressure plate is constructed of a material that
can be heated or cooled.
34. The process chamber of claim 27, wherein the soldering
apparatus comprises a carrier unit on which the pressure plate is
directly or indirectly spring-supported or spring-mounted.
35. The process chamber of claim 34, wherein a spring force exerted
by the pressure plate on the solder group is adjustable.
36. The process chamber of claim 34, wherein the base plate is
adjustable relative to the carrier unit.
37. The process chamber of claim 27, wherein a side of the pressure
plate associate with the base plate is planar or has at least one
projecting step that is in contact with the solder group.
38. The process chamber of claim 37, wherein the at least one
projecting step is planar.
Description
[0001] The present invention relates to a method for producing a
solder connection between a plurality of components in a process
chamber sealed off from its surroundings by heating and melting
solder material which is arranged between the components to be
connected.
BACKGROUND OF THE INVENTION
[0002] The term "components" is taken generally to mean circuit
carriers, substrates, substrate carriers, base plates, workpiece
carriers, mounting carriers or the like made from metal, ceramics,
plastics or other materials or any desired to combinations of
material together with components to be fastened thereto, such as
power semiconductor chips, (semiconductor) assemblies or the
like.
[0003] A method of the type in question is in particular used in
large-area soldering operations, in which for example semiconductor
components, microelectronic components or power semiconductor
chips, such as for example transistors or diodes on printed circuit
boards, IGBTs, MOSFETs or diodes on metallised ceramic substrates
or other circuit carriers are soldered or soldered together, or in
which metallised ceramic substrates are soldered to metallic base
plates and/or heat sinks. Printed circuit boards which are to be
connected to heat sinks may also be soldered in a soldering
apparatus of the type in question.
[0004] In order to achieve an optimum soldering result, effort is
made to heat the molten solder together with the components to be
connected in controlled manner to above the melting point of the
solder, also at an elevated pressure of greater than 1013 mbar, and
then to perform cooling in controlled manner to below the
solidification point of the solder in order to connect the
components together without voids.
[0005] Solder connections are generally produced in a process
chamber which is sealed off from its surroundings, in particular is
evacuatable, in which is arranged a soldering apparatus which
comprises a base plate and a pressure plate, between which is
received a solder group comprising the component(s) and the solder
material. The base plate and the pressure plate are adjustable
relative to one another with regard to the spacing thereof for
exerting a pressure force on the solder group. At the same time,
the pressure plate and/or the base plate may heat and/or cool the
components and the solder material. To this end, the stated plates
may be thermally coupled with appropriate heat sources and/or heat
sinks.
[0006] In general, the components and the solder material, for
example in the form of solder chips or solder powder, are assembled
to form a stack before being introduced into the process
chamber.
[0007] When, as is necessary, the components are handled outside
and/or within the process chamber and also during the actual
soldering operation, there is however a risk, once the molten
solder material has solidified, of the components not being in the
desired position relative to one another. Deviations may occur with
regard both to a lateral position of the components and to the
relative spacing thereof.
[0008] U.S. Pat. No. 4,801,069 A discloses a method and an
arrangement for solder connecting components in a gas atmosphere,
wherein in a first step a solder chip is positioned by means of a
bonding material on a printed circuit board as circuit carrier and
at least temporarily fastened by means of heating, and in a
subsequent step a component to be soldered is temporarily fastened
to the solder chip and the circuit carrier with a further bonding
material with application of pressure prior to a soldering
operation. The operation has multiple stages and involves repeated
heating and cooling of the components, which means that processing
is not only costly in energy terms and involves exposure to high
thermal loads but is also relatively time-consuming. The multistage
arrangement steps can easily result in mispositioning. The
multistage nature of the method means that it cannot be implemented
under a vacuum atmosphere.
[0009] US 2009/0 085 227 A1 proposes a method and an apparatus for
flip chip connection of a component to a circuit carrier, in which
predefined spacing is achieved by a mounting apparatus with a
placement frame which, guided by a vacuum suction device, places a
component to be connected onto a circuit carrier. Once the
component to be connected has been positioned on the circuit
carrier by means of the placement frame, it is connected by heating
a solder powder resin located therebetween, wherein a gas
atmosphere of the solder material is formed which outgasses by
convection, such that only contact surfaces which are to be
connected are soldered. Neither a bonding agent for temporary
alignment and fastening nor further application of pressure during
and after the joining operation are here proposed in order
subsequently to maintain a minimum spacing and orientation relative
to one another.
[0010] U.S. Pat. No. 5,175,410 A discloses a hold-down fixture for
the electrical contact feet of a component to be soldered on a
circuit carrier for chip-on-tape mounting, wherein the hold-down
fixture presses contact feet projecting from the periphery of the
component onto the surface of the circuit carrier during the
soldering operation. Outer bars are intended to press the end
regions to be soldered of the contact feet against the solder pads
of the circuit carrier, while inner bars rest directly against the
package of the component to be soldered. Only selected regions of
the component which are to be connected are therefore pressed
directly onto the circuit carrier, and no predefinable structural
height of the overall solder group is made possible, so controlled
soldering of regions between the component and circuit carrier is
not possible in this manner. The hold-down fixture is only usable
for components with peripheral, externally located contact
feet.
[0011] The problem addressed by the invention is that of providing
a method of the initially stated type in which the components may
be connected together more quickly and inexpensively and with
improved dimensional accuracy.
SUBJECT MATTER OF THE INVENTION
[0012] The problem is solved by a method having the features of
claim 1. Advantageous configurations of the method are the subject
matter of the subclaims.
[0013] The invention proposes that the components to be connected
are provisionally connected with a bonding material to form a
solder group in which the components are fixed relative to one
another in a joining position. This prevents the components from
slipping relative to one another during assembly to form the solder
group and/or during handling of the solder group, for example on
introduction into the process chamber.
[0014] The components are advantageously provisionally connected by
the bonding material by adhesive forces which act at the interfaces
between the bonding material and the components or the solder
material.
[0015] According to one advantageous configuration, the bonding
material is selected such that it evaporates without leaving any
residue during production of the solder connection. As a
consequence, it is ensured that the quality of the solder
connection is not impaired by any residues of the bonding
material.
[0016] The bonding material may be sprayed on over a wide area
before or during positioning of the components on the workpiece
carrier or purposefully applied, for example in the manner of an
X-Y plotter, in spots, lines or over a wide area to previously
determined points and regions provided for this purpose of the
components, of the substrate carrier and/or of the workpiece
carrier. Application of the bonding material is preferably
automatic in order to permit high-throughput mass production.
[0017] The soldering method is preferably carried out with solder
chips or "preforms", wherein it is possible to dispense with the
use of soldering paste which optionally contains flux.
[0018] According to a further advantageous configuration, at an
evaporation pressure which is lower than atmospheric pressure, the
evaporation temperature of the bonding material is lower than the
melting temperature of the solder material at atmospheric pressure
or even at an elevated pressure of above 1013 mbar. As a
consequence, it is ensured that the bonding material can completely
evaporate even before the solder material has melted. It is not
absolutely necessary for this purpose for the evaporation
temperature of the bonding material at atmospheric pressure to be
lower than the melting temperature of the solder material, it may
also be higher.
[0019] A further advantageous configuration provides that the
solder group is heated to an intermediate temperature which is
lower than the melting temperature of the solder material at
atmospheric pressure or also at an elevated pressure of above 1013
mbar, and that the pressure in the process chamber is reduced to a
pressure below the evaporation pressure at the intermediate
temperature, such that the bonding material evaporates. The
pressure in the process chamber may advantageously be reduced only
once the solder group has been heated to the intermediate
temperature. It is, however, also possible to reduce the pressure
even before the intermediate temperature is reached. The pressure
may be reduced continuously or in steps. It should, however, be
ensured that the bonding material has been able to evaporate before
the solder material melts.
[0020] A further advantageous configuration provides that the
pressure in the process chamber is initially reduced to a pressure
above the evaporation pressure of the bonding material at the
intermediate temperature, such that the bonding material does not
yet evaporate, that subsequently a cleaning agent, in particular
methanoic acid, hydrogen or a plasma, is introduced into the
process chamber to clean the solder group, and that subsequently
the pressure in the process chamber is reduced to a pressure below
the evaporation pressure of the bonding material at the
intermediate temperature. Introduction of a plasma into the process
chamber is in particular also taken to mean production of the
plasma in the process chamber itself, wherein a suitable substance
to be ionised may optionally be introduced into the process
chamber. The advantage in this configuration is that, even during
the cleaning operation, there is still a provisional connection
between the components and/or the solder material. On reduction of
the pressure in the process chamber to a pressure below the
evaporation pressure of the bonding material at the intermediate
temperature, the bonding material and the cleaning material can be
jointly discharged from the process chamber.
[0021] Alternatively, it is however also possible initially to
evaporate the bonding material and only then to introduce the
cleaning agent into the process chamber.
[0022] According to a further advantageous configuration, the
intermediate temperature while the pressure in the process chamber
is being reduced to a pressure below the evaporation pressure of
the bonding material may be maintained at a predetermined
temperature value or within a predetermined temperature range at
least until evaporation of the bonding material is complete.
[0023] The stated temperature value or the stated temperature range
are always below the melting temperature at standard pressure or
also at an elevated pressure of above 1013 mbar. As a consequence,
the risk of bonding material still being present on the solder
group while the solder material is melting is further reduced.
[0024] A further advantageous configuration may provide that the
bonding material is arranged in the region of edges and/or corners
and/or the centre or in the centre region of the components to be
connected and/or of the solder material. In this manner, the
bonding material can be applied very simply.
[0025] An advantageous embodiment provides that the solder material
melts once the bonding material has evaporated in order to prevent
contamination of the solder material.
[0026] A further advantageous configuration may provide that the
bonding material is liquid or pasty and in particular comprises a
terpene alcohol, in particular isobornyl cyclohexanol. The desired
liquid or pasty state of matter should prevail at least at room
temperature and atmospheric pressure.
[0027] Suitable mixtures or solutions of various substances may
also be used as the bonding material. In particular, a filler or
thickener may also be added to the bonding material. It should,
however, be ensured that even the constituents of the bonding
material which are optionally solid at room temperature and
atmospheric pressure are capable of evaporating at elevated
temperature and reduced pressure in line with the above-stated
conditions before the solder material has melted.
[0028] A further advantageous configuration provides that, at least
while the solder material is melting, the solder group is received
in a soldering apparatus arranged in the process chamber, wherein
the soldering apparatus has a base plate and a pressure plate,
between which is received the solder group and which are adjustable
relative to one another with regard to the spacing thereof for
exerting a pressure force on the solder group, and has a stop
apparatus which limits the spacing between the base plate and the
pressure plate to a minimum spacing, such that, once the solder
material has melted, the solder group has a predetermined
thickness. The soldering apparatus ensures that the components and
the solder material are preloaded against one another and, once the
solder material has melted, continue to be compressed, since the
molten solder material can spread further between the components
and optionally fill any small interspaces present there. The stop
apparatus here limits the extent of pressing such that, once the
solder material has solidified, the solder group has a defined
thickness or height. Dimensional accuracy is further improved as a
consequence since not only lateral shifts, but also deviations from
a predetermined thickness or height of the component assembly can
reliably be prevented. In addition, in the event of excessively
strong pressing, solder material is prevented from being squeezed
out laterally between the components. The invention differs from
conventionally used soldering frames in that direct physical
contact occurs only briefly, namely while the solder is in the
molten state or at the onset of a solidification phase.
[0029] Permanent or mechanically fixing contact is avoided in order
to avoid damaging or stressing the material.
[0030] The stop apparatus can particularly advantageously be used
in a multichamber system for flow production. Such a system
comprises at least two chambers, in particular three chambers, for
preheating, connecting and cooling. The stop apparatus is
advantageously provided at least in the cooling chamber in order to
ensure mechanical alignment during solidification of the solder.
The stop apparatus may furthermore also be used in the soldering
chamber for connecting the components and may also be used in the
preheating chamber for alignment prior to the joining operation. To
this end, the stop apparatus may advantageously be guided through
the system with a displaceable workpiece carrier.
[0031] According to one advantageous configuration, the stop
apparatus is arranged on the base plate or the pressure plate.
[0032] According to a further advantageous configuration, the stop
apparatus is adjustable, such that the minimum spacing can be set.
This permits variable adaptation of the stop apparatus to different
dimensions or to a different number of components to be
connected.
[0033] A further advantageous configuration provides that the stop
apparatus comprises a plurality of in particular length-adjustable
stop elements. As a consequence, it is possible to ensure that
dimensional accuracy can be maintained over the entire lateral
extent of the solder group. In particular, tilting or tipping of
the pressure and base plates relative to one another can be
avoided.
[0034] According to one advantageous configuration, the stop
elements may have an adjusting device, in particular an adjusting
thread which interacts with a complementary adjusting device, in
particular a complementary thread, provided on the base plate or
the pressure plate. The desired adjustability of the stop apparatus
can be straightforwardly achieved as a consequence.
[0035] A further advantageous configuration provides that the stop
elements are arranged such that, on reaching the minimum spacing,
they bear with a respective free end against a component of the
solder group, against a base frame carrying one of the components
or against the base plate. If the stop elements are intended to
bear against a component of the solder group, said component should
sensibly be a terminating component which as it were forms a bottom
or top of the component stack and projects laterally beyond the
other components of the solder group. The stop elements may,
however, also come to a stop against other assemblies. For
instance, the stop elements which are for example fastened to the
pressure plate may come to a stop against a base frame which is
used as a component carrier, or even against the base plate itself.
The base frame may, for example, carry a circuit carrier as the
terminating component of the solder group.
[0036] Temperature management in soldering and sinter-bonding
processes in electrical engineering and electronics has a major
influence on a product's quality, reliability and service life.
During the solder material cooling phase, solder grains or islands
may be formed as hardening proceeds, wherein material-specific
characteristics such as the modulus of elasticity, the temperature
coefficient of the solder material and the grain shape alignment of
the solder can have a substantial influence on the joint. A fatigue
characteristic of the joint is substantially dependent on the
solder grain size. It has been found in the context of the
invention that grain size and alignment can be purposefully
influenced by purposeful temperature adjustment during the heating
phase but in particular during the cooling phase. It is here
desirable for temperature adjustment to be carried out not only
from beneath the components, but also from above in order to
improve process control. In this manner, any mechanical stresses
which arise between the joined parts can be reduced, alignment
improved and any tendency to warping minimised. According to an
advantageous embodiment, the base plate and/or the pressure plate
is thus heatable and/or coolable. The base plate and/or the
pressure plate may for this purpose have a heat source and/or a
heat sink which may be integrated into the base plate or into the
pressure plate. The base plate and/or the pressure plate may also
be thermally couplable or coupled with a heat source and/or a heat
sink, for example a heating and/or cooling plate. In particular,
the base plate and/or the pressure plate may be configured such
that, in the region of a contact area with the components, they
have a temperature gradient which makes it possible to heat and/or
cool the components in such a manner that regions close to the edge
of the components have a higher temperature than regions remote
from the edge. This makes it possible for the solder material to
solidify from the inside outwards, i.e. towards the edges. During
the cooling process, still liquid solder material can continue to
flow from the outside inwards. As a consequence, it is possible to
avoid the formation of voids and/or cavities in the solder material
due to shrinkage of the volume of the solder material during
cooling. One exemplary configuration of such a device is disclosed
in document WO 2016/091962 A1, the entire disclosure content of
which is included by reference in the present application. In this
manner, the temperature of the components can be purposefully
controlled from above. In this respect, in addition to providing
mechanical alignment, the pressure plate permits temperature
control by purposeful heating and/or cooling of the top of the
components. This may be utilised in particular during sintering, in
particular pressure sintering, as the joining technology, so
enabling both alignment and temperature control even after
departure from the sintering press.
[0037] According to the above-stated exemplary embodiment of a
temperature adjustment function of the base plate and/or pressure
plate, it is particularly advantageous to carry out temperature
adjustment in particular of the pressure plate or of surface
regions of the pressure plate facing towards the top of the
component by means of a thermofluid or by means of one or more
temperature adjustment elements. The thermofluid used may be a
heatable liquid, in particular water or a water-glycol mixture,
preferably at an elevated fluid pressure of 2-3 bar or more, in
order to permit rapid heating or cooling. An electrical temperature
adjustment element, in particular an electrical heating resistor or
a Peltier cooling element or the like, may likewise advantageously
be used. An electrical element may here for example also be used as
a heater and a cooling fluid for cooling or vice versa. A radiant
heater, for example in the form of an infrared emitter, may
likewise be used and in this manner the pressure plate may for
example be heated from above by an IR emitter, advantageously also
nonuniformly by IR spot emitters or by an IR radiation mask which
only allows IR light to pass through and impinge on the pressure
plate at selected to locations. The individual heating and cooling
elements may conveniently be combined. Zone heating during
different process phases and in different regions of the apparatus
is thus possible, in order to achieve end-to-end temperature
control during the joining process both on the bottom and the top
of the components.
[0038] Projecting steps, in particular thermally conductive steps
and projections, but also recesses and depressions, may
particularly advantageously be formed on a temperature-adjustable
pressure plate in order to expose different heights of components
to pressure and to achieve good thermal coupling. The stop elements
may to this end bear directly on the workpiece carrier or the base
plate, or on further component parts such as jigs, component frames
etc. The projections and steps of the cover plate may be
spring-mounted relative to the cover plate, such that the contact
pressure of the steps relative to the component surface is
dependent on a relative spacing of the cover plate from the
component surface. In this manner, it is possible to permit early
temperature adjustment of the component prior to maximum
application of pressure, whereby a solder temperature can be
selectively maintained in the plasticised or in a liquid phase
before a maximum contact pressure is applied.
[0039] It is advantageously possible to provide a plurality of
pressure plates, each equipped with a stop apparatus, which are
height-adjustable and displaceable relative to the workpiece
carrier either jointly or individually. Individual components may
thus be placed under pressure and contacted for temperature
adjustment purposes with a time offset. The pressure plates may in
each case define individual temperature adjustment zones or be set
by a single temperature adjustment medium or a single temperature
adjustment apparatus, such that components can be differently
thermally treated from above in line with their heat capacity. If
the individual pressure plates are individually displaceable, the
contact pressure may be differently set depending on the component
group.
[0040] The stop element(s) of the stop apparatus may be provided
for thermal coupling to with surface regions of the components and
the dimensions and shape thereof may be specifically configured for
nonuniform input or dissipation of heat.
[0041] According to a further advantageous configuration, the
soldering apparatus has a carrier unit on which the pressure plate
is directly or indirectly spring-supported or spring-mounted. In
principle, however, the base plate may alternatively or
additionally be directly or indirectly spring-supported or
spring-mounted. Spring support or mounting in particular ensures
that the stop apparatus, in particular where a plurality of stop
elements are present, can be uniformly supported against a
corresponding opposing surface, i.e. a component, of the base plate
or against the base frame. It is additionally ensured that an
adjusting apparatus, which is provided for adjusting the relative
position between base plate and pressure plate, does not apply an
inadmissibly high pressure force and, as a consequence, potentially
damage the soldering apparatus.
[0042] A further advantageous configuration may provide that the
spring force which the pressure plate exerts on the solder group
can be set. This may for example proceed by interchangeable springs
of different length and/or with a different spring constant.
Adjustable springs which for example set the effective length of
the springs may also be provided. As a consequence, the pressure
force acting on the solder group can be limited in addition to the
pressure force limitation provided by the stop apparatus.
[0043] According to a further advantageous configuration, the base
plate is adjustable relative to the carrier unit. It is accordingly
for example possible to support the carrier unit on the process
chamber, while the base plate can be adjusted. A reversed solution
with a stationary base plate and an adjustable pressure plate is,
however, also conceivable.
[0044] A further advantageous configuration may provide that the
side of the pressure plate associated with the base plate is planar
or has at least one projecting, in particular planar, step which is
in contact with the solder group. The projecting step is
advantageously smaller in cross-section, i.e. in the lateral extent
thereof, than the solder group or the component in contact with the
step, such that a lateral temperature gradient can be produced at
least in the component directly in contact with the step.
[0045] Use of the invention is in particular advantageous in
sintering, preferably in pressure sintering, in which permanent
connection of the components may be achieved by use of pressure at
reduced temperatures. Production faults and inadequate connections
can be reduced markedly by purposefully aligning the components
relative to one another and enabling height control. In particular,
a further purposeful temperature adjustment by means of the stop
apparatus from above, is capable of improving the joining process
to the effect that further process parameters can be purposefully
influenced and optimised.
DRAWINGS
[0046] Further advantageous embodiments of the invention are
revealed by the description and the drawings.
[0047] The invention is described below on the basis of exemplary
embodiments and with reference to the drawings, in which:
[0048] FIGS. 1 & 2 show schematic diagrams of solder groups in
side view and in part in plan view which are provisionally
connected with a bonding material using the method of the
invention,
[0049] FIG. 3 shows a schematic pressure/temperature diagram for
carrying out the method of the invention according to a first
exemplary embodiment,
[0050] FIG. 4 shows a schematic pressure/temperature diagram for
carrying out the method of the invention according to a second
exemplary embodiment,
[0051] FIG. 5 shows a schematic temperature/time diagram for
carrying out the method of the invention according to the first
and/or second exemplary embodiment,
[0052] FIGS. 6 & 7 show schematic, partially sectional side
views of a soldering apparatus of the invention according to a
first exemplary embodiment in various adjustment positions,
[0053] FIG. 8 shows side views of various solder groups, and
[0054] FIGS. 9 & 10 show schematic diagrams of a soldering
apparatus of the invention arranged in a process chamber according
to a second and a third exemplary embodiment;
[0055] FIGS. 11a, b show schematic diagrams of a soldering
apparatus of the invention according to a fourth exemplary
embodiment;
[0056] FIGS. 12a, b show schematic diagrams of a soldering
apparatus of the invention according to a fifth exemplary
embodiment;
[0057] FIGS. 13a, b show schematic diagrams of a soldering
apparatus of the invention according to a sixth exemplary
embodiment;
[0058] FIGS. 14a, b show schematic diagrams of a soldering
apparatus of the invention according to a seventh exemplary
embodiment.
[0059] FIGS. 1 and 2 show components 12A, 12B which are to be
connected together with the assistance of solder material. Solder
material 16, for example in the form of one or a plurality of
solder pads, as are used, for example, in BGAs (Ball Grid Arrays),
is arranged in each case between components 12A and 12B. Components
12A, 12B are in each case stacked on a further component in the
form of a circuit carrier 14, wherein a component 12B lying
directly on the circuit carrier 14 may already in a preceding step
have been connected with the circuit carrier 14 or solder material
16 in as yet unmelted form may likewise have been provided
there.
[0060] The components 12B are identical or somewhat larger in
cross-section than the components 12A and may thus project a little
beyond the latter on all sides. The solder material 16 arranged in
the form of pads, in contrast, is somewhat smaller in cross-section
than the components 12A, such that there are circumferential narrow
cavities along the edges of the components 12A and 12B. In the
region of the corners of the components, bonding material 18 in the
form of small drops, which provisionally connects the components to
form a respective solder group 10, is in each case introduced into
these cavities. The bonding material 18 is preferably liquid or
pasty and in particular comprises a terpene alcohol, in particular
isobornyl cyclohexanol. Isobornyl cyclohexanol is for example
obtainable under the trade name "Terusolve MTPH" from Nippon
Terpene Chemicals, Inc.
[0061] The bonding material 18 fixes the components 12A, 12B
relative to one another in a joining position by adhesion, such
that they are secured at least in a lateral direction against
unintentional slipping or displacement, for example by vibration
during transfer into a process chamber.
[0062] A solder group 10, as shown in FIG. 1 or 2, may then be
introduced into a process chamber which may comprise a soldering
apparatus. FIGS. 9 and 10 show exemplary process chambers which are
explained in greater detail below.
[0063] The process chamber is sealed off from its surroundings and
has respective apparatuses which are capable of modifying the
pressure in the process chamber and of respectively heating or
melting the components 12A, 12B and the solder material 16. Further
apparatuses which are capable of cooling the connected components
12A, 12B back down may furthermore be present in the process
chamber. Alternatively, one or more further process chambers may be
provided, into which one or more solder groups 10 may be
automatically or manually transferred for cooling and/or for
further processing steps.
[0064] A method for producing a solder connection between the
components 12A, 12B will now be described below according to two
different configurations.
[0065] The pressure/temperature diagrams (p/t diagrams) of FIGS. 3
and 4 use arrows to schematically represent changes in pressure and
temperature between various process points. A liquidus curve L
represents the phase boundary between the solid and liquid state of
matter of the solder material 16, for example tin-silver-copper
solder, and extends virtually independently of pressure at a
temperature of approx. 220.degree. C. A phase boundary P indicates
the transition of the bonding material 18 from the liquid phase
into the vapour phase as a function of temperature and pressure,
wherein, above and to the left of the curve, the bonding material
18 is in the liquid phase and, below and to the right of the curve,
it is in the vapour phase.
[0066] For isobornyl cyclohexanol as the bonding material 18, on
which the p/t diagrams shown are based, the boiling point at
atmospheric pressure is between 308.degree. C. and 313.degree. C.
The boiling point of the bonding material can be reduced to below
the melting point of the solder material by reducing the pressure
in the process chamber. This makes it possible to heat the solder
group 10 to close to the melting point of the solder material 16
without the bonding material 18 already evaporating.
[0067] Starting from a process point A, at which atmospheric
pressure and room temperature prevail, initially only the
temperature is raised until, at a process point B, a temperature of
approx. 180.degree. C. is reached.
[0068] In the exemplary embodiment according to FIG. 3, in a
subsequent step the pressure in the process chamber is then reduced
until a process point C at 180.degree. C. and a pressure between 1
and 10 mbar is achieved. The phase boundary P is crossed during the
transition from process point B to process point C, such that the
bonding material 18 evaporates and can be discharged from the
process chamber.
[0069] A cleaning agent, for example methanoic acid or hydrogen may
then be introduced into the process chamber or a plasma may be
introduced or produced in order to clean the components 12A, 12B to
be connected.
[0070] In a following step, the temperature may then be raised from
180.degree. C. to the melting temperature of the solder material 16
of 220.degree. C. or above, such that process point D is
reached.
[0071] In the second exemplary embodiment according to FIG. 4, at
variance with the first exemplary embodiment according to FIG. 3,
once process point B is reached the pressure is simply reduced
until a process point B' is reached which is still just above the
phase boundary P of the bonding material 18, i.e. still within the
liquid phase of the bonding material. Process point B' is for
example located at a temperature of 180.degree. C. and a pressure
between 10 and 100 mbar.
[0072] When process point B' is reached, cleaning agent is, as
previously described, introduced into the process chamber in order
to clean the components 12A, 12B of contamination. In contrast with
the first exemplary embodiment, the bonding material 18 does not
yet evaporate at process point B'. Once cleaning is complete, the
pressure is further reduced at largely constant temperature until
process point C with a temperature of 180.degree. C. and a pressure
of between 1 and 10 mbar is reached. The bonding material 18 now
begins to evaporate and, together with the cleaning agent, is
discharged from the process chamber.
[0073] Under approximately constant pressure, the temperature of
the solder group 10 is then raised until, at process point D, the
liquidus curve L is reached or crossed and the solder material 18
melts and connects with the components 12A, 12B.
[0074] It should be noted at this point that the transition between
the various process points A, B, B', C and D is only schematic.
Temperature and pressure may accordingly at least in places also be
simultaneously changed, such that states need not necessarily
change isothermally or isobarically. However, prior to establishing
the conditions which bring about evaporation of the bonding to
material 18, efforts are made to bring the temperature of the
solder group 10 as close as possible to the liquidus temperature of
the solder material 16 in order as far as possible to minimise the
period of time during which the bonding material 18 has already
evaporated but the components are not yet connected.
[0075] It furthermore goes without saying that pressure deviations
may also occur during the process which are caused by evaporation
of bonding material 18 and/or solvents or cleaning agents, since
any gas which arises can only be cleared from the process chamber
by the corresponding vacuum devices of the process chamber with a
time delay.
[0076] FIG. 5 shows an exemplary temperature/time diagram, on which
the time profile of the solder group temperature is indicated by a
temperature curve T.
[0077] The soldering process may be subdivided into various process
phases P1 to P4 which are indicated accordingly in FIG. 5. Various
regions or time periods in which specific atmospheric states
prevail in the process chamber are furthermore indicated in the
diagram. Regions in which a nitrogen atmosphere is present are
indicated with reference sign N, regions in which a vacuum (with
different pressures) prevails are indicated with the reference sign
V and a region in which a cleaning agent atmosphere is present is
indicated with the reference sign R.
[0078] During a preheating phase P1, the temperature of the solder
group is raised to 160.degree. C. to 180.degree. C. A nitrogen
atmosphere N is present for most of the duration of the preheating
phase P1, wherein a vacuum V is briefly created at the end of the
preheating phase P1.
[0079] Cleaning phase P2 then follows, in which a cleaning agent
atmosphere R prevails and a vacuum V is produced just for a short
time at the end. This short vacuum phase indicates the discharge of
the evaporated bonding material or cleaning agent. The temperature
changes only slightly during the cleaning phase P2.
[0080] The preheating phase P1 and the cleaning phase P2
advantageously proceed in a first chamber (preheating chamber) of a
multichamber system.
[0081] Then, during melting phase P3, the temperature rises to the
melting temperature of the solder material of approx. 220.degree.
C., wherein a nitrogen atmosphere N is initially present which,
once the melting temperature is reached, is replaced by a vacuum V.
At the end of the melting phase P3, nitrogen is again introduced
into the process chamber, wherein this nitrogen atmosphere N is
also maintained during the subsequent cooling phase P4, in which
the temperature is reduced to below 50.degree. C.
[0082] The melting phase P3 advantageously proceeds in a second
chamber (soldering chamber) and the cooling phase P4 in a third
chamber (cooling chamber), wherein the two phases P3 and P4 may
also proceed in a single chamber.
[0083] The individual chambers may advantageously be separated from
one another in gas-tight manner and a conveying device for passing
the workpiece carriers through the individual chambers is provided,
such that higher throughput can be achieved in flow production.
[0084] A soldering apparatus 50 of the invention according to a
first exemplary embodiment is described below with reference to
FIGS. 6 and 7. The stop apparatus described below is advantageously
used at least in the cooling chamber during cooling phase P4 while
the solder is still liquid. A contact pressure may here act on the
top of the components.
[0085] The soldering apparatus 50 comprises a base frame 54 and a
carrier unit 52 connected with the base frame 54. A substrate 14 of
a solder group 10 is placed in the base frame 54 and is preloaded
towards the base frame 54 by pressure springs 72 which bear against
the carrier unit 52. A pressure plate 64 is spring-mounted by means
of pressure springs 70 on the carrier unit 52. The pressure plate
64 has a stop apparatus with a plurality of stop elements 68 which
are length-adjustably fastened to the pressure plate 64 by means of
adjusting threads. A spring-loaded temperature sensor which can
measure the temperature of the substrate 14 is integrated in a
through-hole in the base plate 66.
[0086] Once the solder group 10 has been placed in the base frame
54 and the carrier unit 52 fastened to the base frame 54, the unit
comprising carrier unit 52 and base frame 54 can be inserted into a
retaining unit 56, wherein the base frame 54 is fixed by means of
guide rollers 58, 60 and retaining strips 62.
[0087] The soldering apparatus 50 furthermore comprises a
height-adjustable base plate 66 which can come into direct contact
with the substrate 14 through the base frame 54 which is open at
the bottom.
[0088] The soldering apparatus 50 may be arranged, as will be
explained in greater detail below, in an evacuatable process
chamber.
[0089] The base plate 66 and/or the pressure plate 64 may be
connected with heat sources and/or heat sinks (not shown) which
make it possible to heat or cool the solder group 10. If the base
plate 66 is adjusted in the direction of the arrow (FIG. 7) towards
the pressure plate 64, the circuit carrier 14, including the
components 12A, 12B mounted thereon, is lifted out of the base
frame 54 against the force of the pressure springs 72. After a
specific adjustment travel, the upper component 12B comes into
contact with the pressure plate 64A such that a pressure force is
applied to the solder group 10 and the components 12A, 12B or the
circuit carrier 14 are compressed until the free end of the stop
elements 68 comes into contact with the circuit carrier 14. In this
position shown in FIG. 7, the pressure plate 64 and the base plate
66 have reached their minimum spacing, such that the solder group
10 can be no further compressed. As a consequence, it is possible
according to FIG. 8 to create a solder group 10 which has a defined
height h.
[0090] If, instead of the circuit carrier 14, an auxiliary carrier
plate (not shown) is placed in the base frame 54, on which one or
more components 12A, 12B are merely laid without solder material
and in turn solder material 16 is laid on the components 12A, 12B,
these components 12A, 12B can be provided, before a solder
connection is actually produced, with a coating of melted solder
material 16 which likewise has a defined height h (see FIG. 8). The
pressure plate 64 may for this purpose be provided with a release
agent coating at the contact point with the solder material 16.
[0091] Soldering apparatuses 150, 250 according to a second or
third exemplary embodiment will now be described with reference to
FIGS. 9 and 10 respectively. The soldering apparatuses 150, 250
comprise an evacuatable process chamber 74 which is sealed off from
its environment. In the process chamber 74, an only schematically
represented retaining unit 56 is shown which receives or mounts a
base frame 54. A circuit carrier 14 as a component part of two
solder groups 10 is in turn mounted in the base frame 54.
[0092] The soldering apparatus 150 (FIG. 9) comprises a pressure
plate 64 which is mounted on the process chamber 74.
[0093] The soldering apparatus 250 (FIG. 10) comprises a pressure
plate 64 which is mounted on the base frame 54 in a similar manner
as in the first exemplary embodiment (FIGS. 6 and 7).
[0094] The soldering apparatuses 150, 250 further comprise a
height-adjustable base plate 66 which may come into contact with
the substrate through an opening in the base frame 54. The
substrate with the two solder groups 10 may here be pressed against
the pressure plate 64. On the pressure plate 64 are fastened stop
elements 68 which, once a minimum spacing between the base plate 66
and the pressure plate 64 has been reached, bear on the circuit
carrier 14, such that the solder groups 10 are no further
compressed and thus have a defined height.
[0095] The stop elements 68 may here also be of height-adjustable
construction.
[0096] The pressure plate 64 may be planar (FIGS. 6, 7 and 10) or
according to a variation have one or more projecting steps 76 which
come into contact with the solder groups 10 (FIG. 9). The steps 76
may, as shown in FIG. 9, have a somewhat smaller cross-section such
that they only come into contact with part of the surface of the
uppermost component. As a consequence, a temperature gradient can
be produced within the components.
[0097] Advantageously, various selective cooling concepts in the
context of horizontal alignment may be achieved by the pressure
plate. Selective cooling on completion of the soldering operation
is known in the prior art, for instance concepts involving exposing
a soldered item to coolant vapour from the bottom or mechanically
contacting it with cooling pins. It is thus ensured that, during
the solidification process, the soldering agent solidifies in
defined manner from the inside outwards and thus no voids and
defects are formed in the solder's microstructure. The remaining
FIGS. 11 to 14 (in each case with distant and applied pressure
plate) show various concepts for mechanically contacting a cooling
or heating device with the top of a component in order to permit
selective control of heating or cooling in such a way that the
solidification process of the soldering agent can also be
selectively influenced from above by mechanical connection by the
pressure plate.
[0098] FIGS. 11 to 14 show different embodiments which illustrate
various options for selectively cooling or heating solder groups
uniformly or nonuniformly from the top:
[0099] In FIG. 11a (with spaced pressure plate 64), a step 76 of
the pressure plate 64, which step is coolable or heatable, is being
advanced towards a solder group 10 of stacked components 12 which
are connected by means of solder material 16, see FIG. 11b, in
order to provide cooling/heating from above. Compression travel is
limited by stop elements 68 which bear on the top of a component
frame 82 or jig. The stop plate 64 is guided by a pressure
apparatus retaining to frame 84 which serves as a frame for the
pressure plate 64, wherein the retaining frame 84 may be
alternatively heated or cooled by means of ports 78 for a
thermofluid. The thermofluid may be a pressurised water and glycol
mixture which allows the temperature of the pressure plate to be
rapidly set. The base plate 66, which carries the circuit carrier
14, may likewise be heated or cooled by a thermofluid by means of
ports 78, such that the temperature can be set from both above and
below. Prior to application of pressure, the solder material 16 is
nonuniformly distributed under the solder group 10, such that the
solder group 10 is askew relative to the circuit carrier 14,
resulting in a variable solder distribution. After application of
pressure in FIG. 11b, horizontal alignment may be achieved and
solder material uniformly distributed within and below the solder
group 10.
[0100] In a configuration, modified relative to FIG. 11, of the
exemplary embodiment of FIG. 12a (spaced pressure plate 64) and
FIG. 12b (application of pressure onto the solder group 10), an
overall solder group 10 comprising a plurality of components 12a to
12d is compressed by a single pressure plate 64. The temperature of
the pressure plate 64 is in turn adjusted by a retaining frame 84
through which fluid is passed and the temperature of the base plate
66 arranged beneath the solder group 10 may likewise be adjusted
via the circuit carrier 14. The solder group includes a plurality
of adjacent components 12c, 12d which are sandwiched by larger
components 12a, 12b as base and cover. Aligning the larger
components 12a, 12b, for example cooling plate and backplane,
aligns the smaller components 12c, 12d.
[0101] In the embodiment of a stop apparatus shown in FIGS. 13a,
13b (in respectively open and compressed representation), a
plurality of pressure plates 64a, 64b are provided which may be
separately and individually displaced but may also be jointly
displaced on a retaining frame 84. The pressure plates 64a, 64b in
each case comprise individually settable pressure elements 68,
which may for example have different heights and are separately or
jointly temperature-adjustable by means of fluid ports 78. Thanks
to steps 76, different solder groups 10a, 10b can be compressed on
a substrate carrier 14 in a manner adapted to the height and size
of the surface. In this manner, soldered items 10 of differing
heights can be selectively cooled and aligned. Heating or cooling
capacity can be individually set on different pressure elements.
The various stop elements 76 ensure individually settable stop
heights of the pressure plates 64a, 64b.
[0102] Finally, the embodiment represented in FIGS. 14a, 14b (open
and compressed state) shows a pressure plate 64 without its own
cooling or heating device. The temperature of the pressure plate 64
can be indirectly adjusted via a laterally arranged cooling or
heating device which is integrated in a retaining frame 84 of the
pressure plate 64. The pressure plate 64 may accordingly for
example be integrated in a hold-down device and/or may have its
temperature adjusted by a cooling or heating device arranged
beneath the soldered item. Vertical steps 76 are arranged on the
pressure plate which are capable of selectively bearing on
individual surface regions of the solder group 10 and are capable
of selectively introducing or removing heat. The steps 76
simultaneously serve as stop elements 68. Individual components 12a
may here be compressed and temperature-adjusted while other,
pressure-sensitive components 12b, 12c of the solder group 10 are
left free.
[0103] The embodiments shown in FIGS. 11-14 may be used
individually or in combination and may synergistically complement
and be combined with one another or individually exert their
advantageous effect.
[0104] In all the embodiments of the soldering apparatus 50, 150,
250 (FIGS. 6 to 14), the components 12A, 12B may be provisionally
connected by means of bonding material 18 with one another, with
the solder material 16 and/or with the circuit carrier or substrate
14 in the manner described with reference to FIGS. 1 to 5.
LIST OF REFERENCE SIGNS
[0105] 10 Solder group [0106] 12A, 12B Component [0107] 14
Substrate/circuit carrier [0108] 16 Solder material [0109] 18
Bonding material [0110] 50, 150, 250 Soldering apparatus [0111] 52
Carrier unit [0112] 54 Base frame [0113] 56 Retaining unit [0114]
58, 60 Guide roller [0115] 62 Retaining strip [0116] 64 Pressure
plate [0117] 66 Base plate [0118] 68 Stop element [0119] 70, 72
Pressure spring [0120] 74 Process chamber [0121] 76 Step [0122] 78
Temperature-adjustment fluid port [0123] 82 Component frame [0124]
84 Pressure apparatus retaining frame [0125] A, B, B', C, D Process
point [0126] L Liquidus curve [0127] N Nitrogen atmosphere [0128] P
Phase boundary [0129] P1 Preheating phase [0130] P2 Cleaning phase
[0131] P3 Melting phase [0132] P4 Cooling phase [0133] R Cleaning
agent atmosphere [0134] T Temperature curve [0135] V Vacuum
* * * * *